如何用C语言实现十六进制转换为十进制

#include int convert(char *str,int n) { int w=1,i=0,rt=0; while ( str[i] ) i++; while ( i>0 ) { i--; if ( (str[i]>='0')&&(str[i]<='9') ) rt+=(str[i]-'0')*w; else if ( (str[i]>='a')&&(str[i]<=